The present invention relates generally to rechargeable batteries. More particularly, the invention concerns a rechargeable battery pack that can be easily installed in and removed from a device to be powered without the use of tools and with assurance that the correct polarity of the batteries relative to the requirements of the device will be established.
A wide variety of electrical devices are powered by packs of rechargeable batteries, typically packs containing two or more pairs of conventional "C" or "D" size sealed, rechargeable batteries. A pair of terminals is included for connection with terminals on the device to be powered. Often, these terminals take the form of tabs or connectors on the exterior of the battery pack. Such an arrangement is not particularly desirable since the exposed connectors may be inadvertently, or carelessly, brought into contact with metal objects or surfaces, such as tools, or the frame or housing of the device in which the pack is mounted. This contact can produce a battery-damaging ground or short or can create a spark that will damage the electrical contacts on the battery pack or the object or surface touched. In many applications, the device to be powered includes electronic circuitry that requires a predetermined polarity connection with the batteries. The electrical connectors on battery packs and the configuration of the packs do not always ensure that the packs will be installed so as to provide the correct polarity.
In some applications, the device and battery pack must function under adverse environmental conditions. A rear-of-train telemetry unit that transmits train status information from the rear of the train to the locomotive is a prime example of this type of application. The battery powered unit is mounted on the coupling of the last vehicle of the train and contains an RF transmitter, various sensing devices, and associated electronic circuits. As a result of its positioning, the unit must endure vibration, shock, grime, and extremes of temperature. Although measures are taken to conserve power, the electrical requirements of the system and the environmental factors often necessitate that the batteries be replaced with reasonable frequency. Although the telemetry units may be removed from the vehicle, this is often unfeasible or impractical because of time or locational constraints. As a result, the unit must remain mounted while the batteries are replaced. In adverse weather, this can prove to be a difficult operation or at least one that creates the risk of reversing the polarity of the batteries or causing unwanted contact between the batteries and metallic objects. Even under more hospitable weather conditions, it is not uncommon for the battery packs to be subjected to rough handling that can damage the battery pack and its contacts as well as the electrical contacts in the unit that receives the pack.
From the foregoing, it can be appreciated that it would be extremely desirable to have a rechargeable battery pack that can be installed and removed with ease and with little likelihood of mechanical or electrical damage to the case and batteries or to the device that receives the same. It would be particularly desirable to have such a rechargeable battery pack that further includes an arrangement to prevent the pack from being installed upside down or backwards, i.e., with its electrical contacts connected in reverse with the electrical connections on the unit to be powered.